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    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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    <script>
        async function async1() {
            console.log('async1 start') //2
            await async2()
            // await 的后面，都可以看作是 callback 里的内容，即异步
            console.log('async1 end') // 异步内容先不执行，放到一边，先执行完同步内容再回来执行异步 5
        }

        async function async2() {
            console.log('async2')  // 3
        }


        console.log('script start') // 1
        async1()
        console.log('script end') // 4

    </script>
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